worktree: add per-worktree config files

A new repo extension is added, worktreeConfig. When it is present:

 - Repository config reading by default includes $GIT_DIR/config _and_
   $GIT_DIR/config.worktree. "config" file remains shared in multiple
   worktree setup.

 - The special treatment for core.bare and core.worktree, to stay
   effective only in main worktree, is gone. These config settings are
   supposed to be in config.worktree.

This extension is most useful in multiple worktree setup because you
now have an option to store per-worktree config (which is either
.git/config.worktree for main worktree, or
.git/worktrees/xx/config.worktree for linked ones).

This extension can be used in single worktree mode, even though it's
pretty much useless (but this can happen after you remove all linked
worktrees and move back to single worktree).

"git config" reads from both "config" and "config.worktree" by default
(i.e. without either --user, --file...) when this extension is
present. Default writes still go to "config", not "config.worktree". A
new option --worktree is added for that (*).

Since a new repo extension is introduced, existing git binaries should
refuse to access to the repo (both from main and linked worktrees). So
they will not misread the config file (i.e. skip the config.worktree
part). They may still accidentally write to the config file anyway if
they use with "git config --file <path>".

This design places a bet on the assumption that the majority of config
variables are shared so it is the default mode. A safer move would be
default writes go to per-worktree file, so that accidental changes are
isolated.

(*) "git config --worktree" points back to "config" file when this
    extension is not present and there is only one worktree so that it
    works in any both single and multiple worktree setups.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 79 insertions, 0 deletions

diff --git a/t/t2029-worktree-config.sh b/t/t2029-worktree-config.sh
new file mode 100755
index 0000000..286121d
--- /dev/null
+++ b/t/t2029-worktree-config.sh
@@ -0,0 +1,79 @@
+#!/bin/sh
+
+test_description="config file in multi worktree"
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit start
+'
+
+test_expect_success 'config --worktree in single worktree' '
+	git config --worktree foo.bar true &&
+	test_cmp_config true foo.bar
+'
+
+test_expect_success 'add worktrees' '
+	git worktree add wt1 &&
+	git worktree add wt2
+'
+
+test_expect_success 'config --worktree without extension' '
+	test_must_fail git config --worktree foo.bar false
+'
+
+test_expect_success 'enable worktreeConfig extension' '
+	git config extensions.worktreeConfig true &&
+	test_cmp_config true extensions.worktreeConfig
+'
+
+test_expect_success 'config is shared as before' '
+	git config this.is shared &&
+	test_cmp_config shared this.is &&
+	test_cmp_config -C wt1 shared this.is &&
+	test_cmp_config -C wt2 shared this.is
+'
+
+test_expect_success 'config is shared (set from another worktree)' '
+	git -C wt1 config that.is also-shared &&
+	test_cmp_config also-shared that.is &&
+	test_cmp_config -C wt1 also-shared that.is &&
+	test_cmp_config -C wt2 also-shared that.is
+'
+
+test_expect_success 'config private to main worktree' '
+	git config --worktree this.is for-main &&
+	test_cmp_config for-main this.is &&
+	test_cmp_config -C wt1 shared this.is &&
+	test_cmp_config -C wt2 shared this.is
+'
+
+test_expect_success 'config private to linked worktree' '
+	git -C wt1 config --worktree this.is for-wt1 &&
+	test_cmp_config for-main this.is &&
+	test_cmp_config -C wt1 for-wt1 this.is &&
+	test_cmp_config -C wt2 shared this.is
+'
+
+test_expect_success 'core.bare no longer for main only' '
+	test_config core.bare true &&
+	test "$(git rev-parse --is-bare-repository)" = true &&
+	test "$(git -C wt1 rev-parse --is-bare-repository)" = true &&
+	test "$(git -C wt2 rev-parse --is-bare-repository)" = true
+'
+
+test_expect_success 'per-worktree core.bare is picked up' '
+	git -C wt1 config --worktree core.bare true &&
+	test "$(git rev-parse --is-bare-repository)" = false &&
+	test "$(git -C wt1 rev-parse --is-bare-repository)" = true &&
+	test "$(git -C wt2 rev-parse --is-bare-repository)" = false
+'
+
+test_expect_success 'config.worktree no longer read without extension' '
+	git config --unset extensions.worktreeConfig &&
+	test_cmp_config shared this.is &&
+	test_cmp_config -C wt1 shared this.is &&
+	test_cmp_config -C wt2 shared this.is
+'
+
+test_done